1. Technical Field
The present disclosure relates to an optical waveguide device.
2. Description of the Related Art
In recent years, core communication lines using an optical fiber communication technology have steadily been facilitated. In such a situation, the transmission speed of electric signals in electric devices and data terminals is becoming a bottleneck of an overall communication speed. In an attempt to eliminate such a bottleneck, an optoelectronic composite substrate, where optical signals are used for signal transmission to compensate for the limit of the transmission speed of the electric signals, has been proposed instead of a conventional electric circuit substrate where all the signal transmissions are electrically carried out.
In such an optoelectronic composite substrate, optical signals are transmitted using an optical waveguide configured of a core layer and a cladding layer that surrounds the core layer. In addition, light propagating through the core layer is reflected in a vertical direction by a light path changing mirror that is positioned at an end portion of the optical waveguide.
As an example of the optoelectronic composite substrate, JP-A-2004-235418 and JP-A-2008-152064 disclose that an electric wiring substrate is arranged on the optical waveguide and an optical element is optically coupled with the optical waveguide through an opening portion of the electric wiring substrate.
As explained in the introduction section for explaining the present invention (see later), a first light emitting element and a second light emitting element, which may be arranged on one end side of the optical waveguide, need to be connected to a first driver element and a second driver element, respectively. In this case, the first light emitting element is connected to the first driver element through an upper side wiring layer of the wiring substrate; and the second light emitting element is connected to the second driver element through a lower side wiring layer and a via conductor of the wiring substrate.
In such a structure, when electric signals are transmitted at a high speed, a transmission loss may be caused by, for example, reflection or the like that is caused by the via conductor, which makes a high speed signal transmission unfeasible.
In addition, in the wiring substrate having the via conductor, impedance mismatching may be caused in a transmission line, because dimensional accuracy in the width and thickness of a wiring layer formed by a non-electrolytic plating process tends to be decreased, so that a signal transmission characteristic is degraded.